Wilkinsons catalyst chloride

For practical hydrogenation of olefins four classes of metal complexes are preferred (a) Rh complexes, the RhCl(PPh3)3, the so-called Wilkinson catalyst and the [Rh(diene)-(PR3)2]+ complexes, (b) a mixture of Pt and Sn chlorides, (c) anionic cyanocobalt complexes and (d) Ziegler catalysts, prepared from a transition metal salt and an alkylaluminum compound. 

One last remark concerning the two catalysts we have discussed in more detail, cationic rhodium catalysts and the neutral chloride catalyst of Wilkinson. The difference of the catalytic system discussed above from that of the Wilkinson catalyst lies in the sequence of the oxidative addition and the alkene complexation. The hydrogenation of the cinnamic acid derivative involves a cationic catalyst that first forms the alkene complex the intermediate alkene (enamide) complex can be observed spectroscopically. 

Continuous homogeneous catalysis is achieved by membrane filtration, which separates the polymeric catalyst from low molecular weight solvent and products. Hydrogenation of 1-pentene with the soluble pofymer-attached Wilkinson catalyst affords n-pentane in quantitative yield A variety of other catalysts have been attached to functionalized polystyrenes Besides linear polystyrenes, poly(ethylene glycol)s, polyvinylpyrrolidinones and poly(vinyl chloride)s have been used for the liquid-phase catalysis. Instead of membrane filtration for separating the polymer-bound catalyst, selective precipitation has been found to be very effective. In all... 

The second transition series from yttrium to silver all have a partially filled 4d-orbital. This includes cadmium, but similarly to zinc, cadmium has no partially filled d-orbitals therefore, it is not technically considered among the T-metals. All the second transition series elements except for yttrium form important compounds such as the Wilkinson catalyst -rhodium(I)tris-(triphenylphosphine)chloride, [Rh a) (flWis), ... 

Development by Geoffrey Wilkinson of a soluble catalyst for hydrogenation [tris(triphenylphosphine)rhodium chloride, Section 7.13 and Special Topic G] led to Wilkinson s earning a share of the 1973 Nobel Prize in Chemistry. His initial discovery, while at Imperial College, University of London, inspired many other researchers to create novel catalysts based on the Wilkinson catalyst. Some of these researchers were themselves recognized by the 2001 Nobel Prize in Chemistry, 50% of which was awarded to William S. Knowles (Monsanto Corporation, retired) and Ryoji Noyori (Nagoya... 

The Wilkinson catalyst is a complex of rhodium(I) and triphenylphosphine. It is prepared by refluxing rhodium(III) chloride with excess triphenylphosphine in ethanol. The initial product, Rh(PPh3)3Cl, loses a molecule of triphenylphosphine at the beginning of the catalytic cycle (Figure 17.8). 

The avermectins also possess a number of aUyflc positions that are susceptible to oxidative modification. In particular the 8a-methylene group, which is both aUyflc and alpha to an ether oxygen, is susceptible to radical oxidation. The primary product is the 8a-hydroperoxide, which has been isolated occasionally as an impurity of an avermectin B reaction (such as the catalytic hydrogenation of avermectin B with Wilkinson s rhodium chloride-triphenylphosphine catalyst to obtain ivermectin). An 8a-hydroxy derivative can also be detected occasionally as a metaboUte (42) or as an impurity arising presumably by air oxidation. An 8a-oxo-derivative can be obtained by oxidizing 5-0-protected avermectins with pyridinium dichromate (43). This also can arise by treating the 8a-hydroperoxide with base. 

The Noc group, developed for amino acid protection, is introduced with the acid chloride (Et3N, H2O, dioxane, 2 h, 20°, 61-95% yield). It is cleaved with Pd(Ph3P)4 (THF, A, A -dimethyibarbituric acid, 8 h, 20°, 80% yield). It is not isomerized by Wilkinson s catalyst, thus allowing selective removal of the allyl ester group. 

Wilkinson s catalyst has also been reported to decarbonylate aromatic acyl halides at 180°C (ArCOX ArX). This reaction has been carried out with acyl iodides, bromides, and chlorides. Aliphatic acyl halides that lack an a hydrogen also give this reaction, but if an a hydrogen is present, elimination takes place instead (17-16). Aromatic acyl cyanides give aryl cyanides (ArCOCN—> ArCN). Aromatic acyl chlorides and cyanides can also be decarbonylated with palladium catalysts. °... 

Several techniques have been used to activate the zinc metal and improve yields. For example, pretreatment of zinc dust with a solution of copper acetate gives a more reactive zinc-copper couple.168 Exposure to trimethylsilyl chloride also activates the zinc.169 Wilkinson s catalyst, RhCl(PPh3)3 catalyzes formation of Reformatsky reagents from diethylzinc, and reaction occurs under very mild conditions.170... 

In transfer hydrogenation with 2-propanol, the chloride ion in a Wilkinson-type catalyst (18) is rapidly replaced by an alkoxide (Scheme 20.9). / -Elimination then yields the reactive 16-electron metal monohydride species (20). The ketone substrate (10) substitutes one of the ligands and coordinates to the catalytic center to give complex 21 upon which an insertion into the metal hydride bond takes place. The formed metal alkoxide (22) can undergo a ligand exchange with the hydride donor present in the reaction mixture, liberating the product (15). 

The mechanism for the addition of 50 to anthraquinone (Scheme 52), 1,4-diacetylbenzene (Scheme 53), and 1,2-diacetylbenzene (Scheme 54) has been proposed.326 The addition of 50 to benzophenone followed by reaction with Wilkinson s catalyst formally results in the hydrogenation of a double bond (Equation (262)).325 This species also undergoes stereospecific inertion into the vinyl chloride bond of various halogenated alkenes with high yields in most cases (Equations (263)-(267)).329... 

The tritium labelled V.fischeri AHL 31 was prepared with a specific activity of 45-55 Ci/mmol by the tritiation of the corresponding unsaturated precursor, AT-(3-oxo-4-hexenoyl)-L-HSL 30 in the presence of a homogeneous Wilkinson s catalyst, tris(triphenylphosphine)rhodium[I] chloride (Scheme 13) [71]. 

Work with supported ionic liquids was extended to a cationic polymer, poly (diallyldimethylammonium chloride), which has quaternary ammonium functional groups (Fig. 16) 268). The extra-structural counter anion is Cl . The polymer was applied to simultaneously incorporate an ionic liquid and a transition-metal catalyst via a simple mixing of the components. Wilkinson s catalyst and [BMIM]PF6 were... 

Reaction of cyclobutanecarbaldehydes with tris(triphenylphosphane)rhodium(I) chloride (Wilkinson s catalyst) gives the decarbonylated compounds in moderate yields.9,10,12 14 For example, (l/ ,25, 3R)-3-acetoxymethyl-2-tci7-butyfdiphenyfsiloxycyclobutanecarbaldehyde was refluxed with the catalyst to give (l/ ,2/ )-l-acetoxymethyl-2-/tr/-butyldiphenylsiloxycyclobu-tane (6).9... 

Wilkinson and co-workers (3) showed that the maximum activity of the tertiary phosphine rhodium(I) chloride catalysts occurred at a ligand. -rhodium ratio of about 2. This ratio was used in the systems studied for the effects of hydrogen pressure (Table I). In the triphenyl-phosphine system (abbreviated as L°), the rate of hydrogenation increased with pressure in the accessible pressure range, in accord with previous observations (2) by Wilkinson and co-workers. However, with the p-dimethylamino substituted tertiary phosphines L1 and L2 the rates of hydrogenation were essentially independent of the hydrogen pressure within the experimental errors. For tris (p-dimethylaminophenyl) phos-... 

The tris(triphenylphosphine)rhodium chloride catalyst was prepared according to the procedure of G. Wilkinson and co-workers.4... 

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